1. Field of the Invention
The invention relates to a rotary dobby for a loom, and to a loom fitted with such a dobby. The invention also relates to a subassembly belonging to such a dobby, and to a method of controlling such a dobby.
2. Brief Description of the Related Art
It is known, e.g. from EP-A-1 111 106, to fit a rotary dobby with two compression latches serving to couple a drive disk to an eccentric which forms an actuator element for actuating a swinging link coupled to a heddle frame. Overall that equipment gives satisfaction.
When a lifting unit is coupled to the rotary movement of the main shaft of a dobby, the forces transmitted between the disk and the eccentric pass in alternation from one latch to the other. One latch transmits the drive force for driving the lifting unit, while the other is driven by the return force that corresponds to the energy returned by the lifting unit to the main shaft. The driver latch operates during the driver stage in the movement of the main shaft, i.e. when the acceleration and the speed of the connected frame have the same sign. The driven latch is loaded during the driven stage of the motion from the main shaft, i.e. when the acceleration and the speed of the frame are of different signs. A connected frame performs a go-and-return movement in one complete rotation of the main shaft. It is possible to decouple the movement of the main shaft when it reaches a selection range, in the vicinity of its two extreme positions. These selection ranges correspond to force being transferred between the latches that work respectively during the driving stage and during the driven stage.
When a lifting unit is in motion, the latches are engaged in a corresponding notch of the drive disk and they bear against corresponding surfaces of the disk. When it is appropriate to stop a lifting unit, the selection device thus needs to act on the latches in order to disengage them from said notches, even though the latch that is working during the driven stage is heavily loaded. The reader arm therefore needs to act powerfully and quickly on the latch, which requires the means for acting on the latches to be dimensioned so as to accommodate the intense forces that are to be delivered. As a result, the latch control elements present a large amount of inertia, and that can limit the operating speeds of known dobbies.